Using space technology, scientists have developed
extraordinary ceramic photocells that could repair malfunctioning
human eyes.

January
3, 2002: Rods and Cones. Millions of them are in the back
of every healthy human eye. They are biological solar cells in
the retina that convert light to electrical impulses -- impulses
that travel along the optic nerve to the brain where images are
formed.

Without them, we're blind.

Indeed, many people are blind -- or going blind -- because
of malfunctioning rods and cones. Retinitis pigmentosa and macular
degeneration are examples of two such disorders. Retinitis pigmentosa
tends to be hereditary and may strike at an early age, while
macular degeneration mostly affects the elderly. Together, these
diseases afflict millions of Americans; both occur gradually
and can result in total blindness.

"If we could only replace those damaged rods and cones
with artificial ones," says Dr. Alex Ignatiev, a professor
at the University of Houston, "then a person who is retinally-blind
might be able to regain some of their sight."

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Years ago such thoughts were merely wishful. But no longer.
Scientists at the Space Vacuum Epitaxy Center (SVEC) in Houston
are experimenting with thin, photosensitive
ceramic films that respond to light much as rods and cones do.
Arrays of such films, they believe, could be implanted in human
eyes to restore lost vision.

"There are some diseases where
the sensors in the eye, the rods and cones, have deteriorated
but all the wiring is still in place," says Ignatiev, who
directs the SVEC. In such cases, thin-film ceramic sensors could
serve as substitutes for bad rods and cones. The result would
be a "bionic eye."

The Space Vacuum Epitaxy Center is a NASA-sponsored Commercial
Space Center (CSC) at the University of Houston. NASA's Space
Product Development (SPD) program, located at the Marshall Space
Flight Center, encourages the commercialization of space by industry
through 17 such CSCs. At the SVEC, researchers apply knowledge
gained from experiments done in space to develop better lasers,
photocells, and thin films -- technologies with both commercial
and human promise.

Below: A schematic diagram of the retina
-- a light-sensitive layer that covers 65% of the interior surface
of the eye. SVEC scientists hope to replace damaged rods and
cones in the retina with ceramic microdetector arrays. Image
courtesy A. Ignatiev.

Scientists
at Johns Hopkins University, MIT, and elsewhere have tried to
build artificial rods and cones before, notes Ignatiev. Most
of those earlier efforts involved silicon-based photodetectors.
But silicon is toxic to the human body and reacts unfavorably
with fluids in the eye -- problems that SVEC's ceramic detectors
do not share.

"We are conducting preliminary tests on the ceramic detectors
for biocompatibility, and they appear to be totally stable"
he says. "In other words, the detector does not deteriorate
and [neither does] the eye."

Crafting such films is a skill SVEC scientists learned from
experiments conducted using the Wake Shield Facility (WSF) --
a 12-foot diameter disk-shaped platform
launched from the space shuttle. The WSF was designed
by SVEC engineers to study epitaxial film growth in the ultra-vacuum
of space. "We grew thin oxide
films using atomic oxygen in low-Earth
orbit as a natural oxidizing agent," says Ignatiev. "Those
experiments helped us develop the oxide (ceramic) detectors we're
using now for the Bionic Eye project."

The ceramic detectors are much like ultra-thin films found
in modern computer chips, "so we can use our semiconductor
expertise and make them in arrays -- like chips in a computer
factory," he added. The arrays are stacked in a hexagonal
structure mimicking the arrangement of rods and cones they are
designed to replace.

The natural layout of the detectors solves another problem
that plagued earlier silicon research: blockage of nutrient flow
to the eye.

"All of the nutrients feeding the eye flow from the back
to the front," says Ignatiev. "If you implant a large,
impervious structure [like the silicon detectors] in the eye,
nutrients can't flow" and the eye will atrophy. The ceramic
detectors are individual, five-micron-size units (the exact size
of cones) that allow nutrients to flow around them.

Artificial retinas constructed at SVEC consist of 100,000
tiny ceramic detectors, each 1/20 the size of a human hair. The
assemblage is so small that surgeons can't safely handle it.
So, the arrays are attached to a polymer film one millimeter
by one millimeter in size. A couple of weeks after insertion
into an eyeball, the polymer film will simply dissolve leaving
only the array behind.

The first human trials of such detectors will begin in 2002.
Dr. Charles Garcia of the University of Texas Medical School
in Houston will be the surgeon in charge.

"An incision
is made in the white portion of the eye and the retina is elevated
by injecting fluid underneath," explains Garcia, comparing
the space to a blister forming on the skin after a burn. "Within
that little blister, we place the artificial retina."

Left: These first-generation ceramic thin film microdetectors,
each about 30 microns in size, are attached to a polymer carrier,
which helps surgeons handle them. The background image shows
human cones 5-10 microns in size in a hexagonal array. Image
courtesy A. Ignatiev.

Scientists aren't yet certain how the brain will interpret
unfamiliar voltages from the artificial rods and cones. They
believe the brain will eventually adapt, although a slow learning
process might be necessary -- something akin to the way an infant
learns shapes and colors for the first time.

"It's a long way from the lab to the clinic," notes
Garcia. "Will they work? For how long? And at what level
of resolution? We won't know until we implant the receptors in
patients. The technology is in its infancy."

Ignatiev has received over 200 requests from patients who
learned of the studies from earlier press reports. "I'm
extremely excited about this," he says. He cautions that
much more research is needed, but "it's very promising."

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